Means for safeguarding electric igniters of blasting detonators against accidental firing



Sept, 24, 946. H. J. ROLFES 2,408,325

MEANS FOR SAFEGUARDING ELECTRIC IGNITERS OF BLASTING nEToNAToRs AGAINST ACCIDENTAL FIRING Filed Aug. 18, 1942 2 Sheets-Slime?. 1

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24, 4. H, 1 Rolf-E5 ZS MEANS FOR SAFEGUARDING ELECTRIC IGNITERS OF BLSTING DETONATORS AGAINST ACCIDENTAL FIRING Filed Aug. 18, 1942 2 Shse$-5heet 2 Y Patented Sept. 24, 1946 MEANS FOR SAFEGUARDING ELECTRIC IGNITERS OF BLASTING DETONATORS AGAINST ACCIDENTAL FIRING Hans Jay Rolfes, Melrose, Johannesburg, Transvaal, Unionof South Africa Application August 18, 1942, Serial No. 455,236. In the Union of South Africa September 11,

1941 15 Claims.

This invention relates to means for safeguarding the electric igniters of blasting detonators against accidental firing by electric currents or spark discharges produced respectively in, or in the vicinity of, the firing means of the igniter by atmospheric electricity.

This application is a continuation in my copending application No. 422,453.

It is obvious that a possible solution to this problem is to surround the two electric leads of the igniter at a position a safe distance from the ring means thereof by a grounded mass of a material which may be termed the ideal material, and which will exhibit a high resistance at voltages of the magnitude used for intentionally iiring the igniter and a low resistance at voltages of the magnitude of the electrostatic charges which produce the currents and spark discharges aforesaid. One means of obtaining a solution oi the problem has already Abeen proposed, viz. to employ, as the grounded material, any material such as, e. g., galena, yellow crystalline iron pyrites or Zincite which has the characteristic that its resistance to electric currents or discharges is an inverse function of the voltage applied. Another means is described in my co-pending patent application No. 422,453,.viz. to employ a part of material, such as aluminum flakes, which offers la complete or substantially complete resistance to voltages of the magnitude used for intentionally firing the igniter and which, on its being subjected to voltages of the magnitude of electrostatic charges caused by atmospheric electricity, becomes locally conductive through coherer action along a path or paths permitting the passage therethrough f the high Voltage charge.

In any of these cases, it will be understood, it is important that the path or paths to ground afforded by the mass of material (which may be --termed the safeguarding means) to high voltage charges should be such as to ensure that, as far as possible, the whole charge passes instantaneously to ground, Without leaving any residual charge in one lead or the other which would produce a iloW of current in the firing means, e. g. bridge-wire, sucient to heat the latter to incandescence.

According -to the present invention, means for safeguarding the electric igniters of blasting detonators as aforesaid comprises teeth, projections,

yedges or other means adapted to constitute dis'- charge points which promote or facilitate the discharge of the high voltage charge from the leads or either of them into the mass.

'The teeth, projections, edges or other means adapted to constitute the discharge points may be formed or provided on bared parts of the electric leads (i. e. the wires of the igniter, fuzehead or other ring means, or the wires of the blasting circuit, or insulated conductorsled 01T from .the said Wires) and/or on the interior of the casing containing the aforesaid mass adjacent to the leads.

If the said teeth, projections, edges or other means are formed or provided on the leads, those on the one lead are preferably directed outwardly and away from those on the other lead so as to promote, in respect of each lead, the high voltage discharge in a radial path through the mass to the igniter shell or ground. The teeth, projections, or equivalent means are particularly effective as a safeguard against a high voltage elec- I trical surge arising in one lead only, since the teeth, projections or other means provided on or associated with that lead ensure the discharge of the whole surge direct to ground, Without any residual surge passing on to the bridge-wire or other firing means suicient to heat the latter to incandescence. In particular, this is an important safeguard for series blasting, where there is especial danger of a surge being set up in the one lead and causing premature firing in the manner stated.

The invention will now be described by way of example with reference to the annexed drawings, in which: Y

Fig. 1 is a sectional view in elevation of an instantaneous electric detonator embodying the invention.

Fig. 2 is a sectional view in elevation of an instantaneous electric detonator, enclosed in an inert body or so-called Wax primer, embodying the invention.

Figs. 3, 4 and 5 are sectional views in elevation of electric igniters for delay-action detonators, embodying the invention.

Fig. 6 is a diagrammatic view of an alternative means for associating the discharge points and safeguarding mass indirectly with the igniter leads.

Figs. 7 and 8 are diagrammatic views of two embodiments of this alternative means applied to a group of detonators connected in series.

Figs. 9 and 10 are respectively a sectional elevation, and a sectional plan, of a convenient practical form of the alternative means.

Fig. 11 is a view of the alternative means showing an arrangement of teeth, projections or the like in or on vthe interior of the casing contain- 3A ing the safeguarding mass, instead of on the leads.

Referring to Figs. 1 to 5:

In Fig. l, the insulated electric leads Ia, Ib pass through a rubber plug 2 crimped in the mouth of the copper or other conductive shell 4 of the detonator. In the usual manner the detonator shell 4 contains a fuZe-head 5, a primary charge B and secondary charge 1. The fuze-head 5 has a bridge-wire 8 within the igniter composition or bead thereof, and the one end of the bridge-wire 8 is connected to a bridge-pole 9 andthe other end to a bridge-pole I0. These poles A9, II) are connected at soldering points II, I2 to"the respective leads le, Ib.

The leads Ia, Ib are bared at parts I3, Hirespectively spaced from the fuze-head 5 outside the zone of sensitivity thereof. The parts I3, I4 pass through a plug I5 provided within the detonator shell 4 between the rubber plug 2 and the insulating sleeve or body I5 of the fuzehead 5. I

The plug I5, hereinafter referred to as the safeguarding plug,-may be a coherer plug, as described in my co-pending patent application No. 422,453, or a plug consisting of galena or other material having the characteristic that Aits resistance to electric currents or discharges Ais an inverse function of the applied voltage, or any other material, such as aluminum flakesVwhich exhibits a high resistance at voltages of the magnitude used for intentionally iiring the igniter and a low resistance at voltages of the magnitude of the electrostatic charges which produce the currents and spark discharges aforesaid.

The bared parts I3, I4 of the leads la, Ib are formed with pointed teeth I1, IB respectively directed diametrically outwards towards the wall of the detonator shell 4. Any projections, edges or other` means adapted to constitute discharge points may be employed in lieu of the particular teeth I1, I8 illustrated, so long as they fulfil the purpose of promoting discharge of a high voltage charge from the leads Ia, Ib, or either of them, into the safeguarding plug I5.

When the detonator is fired, the ring current passes in the normal manner through the one lead, say Ia, across the bridge-wire 8, and out through the other lead Ib, the bridge-wire being heated to incandescence and ring the igniter bead of the fuZe-head 5. In other words, to the voltage of the magnitude used for the ring current, the safeguarding plug I5 reacts as an linsulator. If, on the other hand, an electrostatic charge of high potential is induced in the firing circuit consisting of the leads Ia, ib and bridgewire 8, or if this circuit is struck by a lightning discharge, the plug I5 permits the passage of the high voltage charge along outward radial paths from the teeth I1, I8 to the wall of the detonator shell 4, and thence to ground. In this manner the ring circuit discharges its high potential to ground without any ow of current being produced in the bridge-wire 8, or spark discharges being produced in the vicinity of the` fuZe-head 5, such as would cause incandescence of the bridge-'wire or premature ignition of the fune-head.

By means of the teeth I1, I8 or similar discharge points, an effective safeguard is also provided against the consequences of a high voltage electric surge which may arise in one lead only of the detonator. The discharge teeth (say the teeth I1 if the surge arises in the lead la) effect complete discharge of that surge direct to the 4 detonator shell 4, without any residual surge passing on to the bridge-Wire In this case, also, therefore, there is no flow of current through the bridge-Wire such as might cause incandescence and premature firing of the fuZe-,head 5.

Fig. 2 shows the application of the invention to a detonator enclosed in an inert body or socalled wax primer 20. Reference numerals used in this figure similar to those used in Fig. 1 refer to similar parts. In this embodiment, the safeguarding plug or mass 2| is made in the form of a layer interposed between the inert or wax body 20 and a top inert or wax layer 22. The leads la, Ib.: are bared and formed with outwardly directed discharge teeth at 23 and 24 respectively, where they pass through the safeguarding layer 2I.

In function, the embodiment shown in Fig. 2 is similar to that already described with reference to Fig. l, and, as shown in Fig. 2, the toothed and bared parts 23, 24 of the leads IE, Ib are preferably spaced outwardly from each other `in the safeguarding layer 2| so as to afford the high voltage discharges a readier path to ground, i. e. to the rock or side `of the borehole in which the wax primer is inserted. y

In Fig. 3, similar numerals again denote similar parts. The embodiment shown inthisiigure is an electric igniter having a copper or otherconductive cylindrical shell 30 into the lower open end of which there is crimped a flexibledelay fuze 3|, of which the other end (not shown) is crimped in known manner in the mouth of a detonator. A safeguarding plug 32 is in this instance inserted in the igniter shell 30 so as to surround the solder points II, I2, the adjacent parts of the bridge-poles 9, I, and the bared and toothed `lower ends 33, 34 of the leads la, Ib. The upper end of the igniter shell 3,0 is closed by Va rubber plug 35 crimped therein.

In any of vthe embodiments of the invention, more than one pair of sets of discharge'points enclosed in a corresponding grounded plug or mass may be used in association with the one detonator or igniter. This modification is shown incorporated in the embodiment illustrated in Fig. 3, where, in addition to the safeguarding plug 32 surrounding the toothed parts 33, 34 of the leads within the igniter shell 30, a second safeguarding plug 36 is contained in a' separate copper or other conductive sleeve or shell 31 which is crimped on rubber plugs'38, 39 as anindependent :unit around Vbared and toothed parts 40, 4I of the leads la, Io outside the igniter shell 30.

When more than one grounded safeguarding plug or mass is thus used, discharge of high voltage charges from the iirng circuit to ground may take place through either one or other'or both of the said plugs or masses. If the safeguarding plug consists of a coherer plug as described in my co-pending application No. 422,453, steps may, if necessary, be taken to ensure that high voltage discharges, should they occur, will not take place through the coherer mass from one lead of the igniter or detonator across to the other.

one another of the sets of 'the discharge points in the respective leads as shown in'Figs. l to 3.

'As an additional safeguard in such cases, how- A safeguard against this happening is the outward direction away from tive leads vand the detonator shell or ground, or inserting between the leads within the coherer mass (as in the case of the upper coherer plug 36 in Fig. 3) a paper sheet 42 or other insulating element.

Fig. 4 shows the application of the invention to a delay-action detonator of the Eschbach type. The construction of this detonator is similar to that of the instantaneous detonator shown in Fig. 1, with the exception that between the fuzehead 5 and the primary charge 6, a delay composition 3la (e. g. antimony and potassium perinanganate) contained in a lead body SIb is provided. Otherwise, similar reference numerals in the two gures denote similar parts.

-In cases where the safeguarding plug or mass is not a coherer plug as aforesaid, but consists e. g; of a galena or like plug having the characteristic that its resistance is an inverse function of the applied voltage, another safeguard against a high voltage charge in one lead producing a dangerous flow of current through the fuze-head 5 is obtained by distributing, equalising or shunting the charge between that lead and the other lead across the portion of the safeguarding plug located between the discharge points of the leads, the discharge across the leads in these cases, i. e. cases other than those in which the safeguarding plug is a coherer plug not resulting in the resistance of the material between the leads being permanently reduced below the value necessary to prevent short-circuiting between the leads, through the safeguarding mass, of the ordinary firing current. Y.

rIfhis modification is shown in Fig. 5, where, in addition to the discharge points 33, 34 surrounded by thesafeguarding plug 32, auxiliary discharge points 43, 44 are formed on the leads la,

Ib respectively with their teeth or points directed towards each other and embedded in an auxiliary safeguarding plug 45, which may be termed an equalising or distributing plug. This plug 45 is insulated from the copper or other conductive enclosing shell 46, or ground, e. g. by a rubber or other insulating sleeve or tube 41. The shell 46 is closed at `the top by a rubber plug 38 4crimped in the mouth thereof and is joined at the bottom to the top end of the igniter shell 30 by crimping 48, the two plugs 32 and 45 being separated and insulated from each other by an intervening rubber plug 49 through which the leads la, Ib pass. With this construction, the equalisation of high voltage charges, between the leads I, Ib is effected in the upper or insulated plug 45, and the discharge to ground is effected vthrough the lower or grounded plug 32, the discharges across the leads, and from the leads to ground, being facilitated in the particular directions desired in both instances.

The grounding or discharging function and the equalising or distributing function may, if

desired, be performed by a single grounded plug lating casing.

While, in the drawings7 the soldering points I l and l2 are shown within the safeguarding plug,

these points may be outside the said plug and insulated from each other and from the igniter shell by being surrounded by a rubber or similar plug.

Referring to Figs. 6 to 11:

In these figures, an alternative means of assooiating the discharge points and safeguarding plug with the igniter leads is illustrated, such means comprising, generally, a safeguarding plug or plugs and discharge points which are not directly in the length of the leads but which are associated with bared ends or parts of insulated conductors led from the respective igniter leads.

Fig. 6 shows the application of this indirect means to a single detonator. The leads 50, 5l of the detonator 52 are respectively tapped by insulated conductors 53, 54, the toothed-ends or discharge points 55, 56 of which are bared and surrounded by a safeguarding plug 51 contained in a grounded metal casing 58. Desirably, but not necessarily, the casing58 is electrically connected to the detonator 52 by a conductor 59 and conductive sleeve 60. This ensures that the detonator casing is not at a lower potential than the discharge casing 58 and that therefore discharge to ground will not take place through the detonator shell in preference to the casing 58.

Fig. '1 shows the application of the same means to a group of series-connected detonators 6 I The insulated conductors 53, 54 are in this instance led from the wires 50a, 5Ia of the blasting cable', and the grounded casing 58 is connected by separate conductors 59a, 59b and sleeves 60a, 60lo to the 'rst and last detonators of the series respectively.

Otherwise the arrangement is similar to that described with reference to Fig. 6.

Fig. 8 shows another application of the said means to a similar group of series connected detonators 62. The insulated conductors 53a, 54EL are led from the blasting wires 50a, 5Ia and their double-direction discharge points 55a, 56a inserted into separate safeguarding plugs 51a, 51b contained in separate grounded casings 56a, 58h. lThis is a specially effective safeguard against short-circuiting of the firing current, e. g. between the bared ends 55, 56 (Fig. 7) of the conductors 53, 54 through the safeguarding plug 51 if it consists of a coherer mass as described in my co-pending patent application aforesaid.

The outside arrangement of the safeguarding plug shown in the preceding Figs. 6 to 8 necessitates that the construction of the plug should be robust, in order to withstand rough handling. In particular, the internal spacing of the discharge points and the casing of the plug must not be disturbed during the charging operations. A rigid and easily made assembly is illustrated in Figs. 9 and 10. In this assembly, the discharge points 55, 56 of the conductors 53, 54 are constituted by two strips 83, 64 of metal foil secured by an adhesive to the opposite sides of an I shaped piece 65 of cardboard or like insulating material, which is a neat lit into the metal casing 66. This insulating piece 65 Yserves to position, and to maintain in position, the strips 53, 64 with respect to the wall of the casing 66, which is itself closed at top and bottom by sealing means 61, 68 held in place by crimping 69, 1S. In the construction shown in Figs. 9 and 10, a copper wire 1I is soldered at one end to the casing 66 and at its other end to a copper ring or sleeve 12, for connection to the detonator casing (as already described with reference to Fig. 6).

have been shown as formed on the leads or conductors,they may be formed `or provided on the casing'of the discharge With their points proj ect-V ing towards the leads, which may be either plain or themselves formed or provided with a complementary set of discharge points. Fig. 11 shows an outside safeguarding plug 13 with the discharge points constituted by copper strips 'M of Yzig-zag form placed parallel and adjacent to plain bared conductors l5, '16, and in contact with a conductive casing 11.

With the present invention, an electric detonator is obtained Which is substantially safe against stray currents and which in addition is equally applicable to series, as to parallel, blasting.

In the appended claims, the term electric leads is to be understood as including the Wires of the igniter and/or the Wires of a blasting circuit, and/or conductors led from these Wires.`

I claim: l y

l. Means for safeguarding thering means of blasting detonators against static charges, including a safeguarding material of a nature to provide high resistance against current voltages for intentional iiring and low resistance to higher voltages of a static charge, means for grounding said safes guarding means, electric leads for the iring means, said leads having bared parts surrounded by the safeguarding material at a distance from the ring means, and discharge points in electrical continuity with said bared parts of such leads to thereby increase the static voltage discharge through said material.

2. .A construction as dened in claim l, wherein the discharge points are in the shape of a series of teeth projecting in opposite directions relative to the leads. fr

3. Means for safeguarding the ring means of blasting detonators against static charges, including a safeguarding material of a nature to provide high resistance against current voltages for intentional firing and low resistance to higher voltages of a static charge, a shell enclosing said ring means and containing said material, means for grounding the material through said shell,

electric leads Within said shell for the ring` means, said leads within said material being bared and formed in such bared parts with discharge points extending from the respective leads toward but free of contact with said shell.

4. Means for safeguarding electric igniters of blasting detonators against static charges otherwise capable of firing the igniter, including a safeguarding material of a nature having a high resistance to normal firing voltages and a low resistance to higher voltages of a static charge,

a shell for said material Wholly free of and beyond the igniter, a pair of electric leads for the igniter, each of said leads leading respectively to and within said shell and having bared parts surrounded by said material within said shell, said shell being grounded, the bared part of each of said leads being provided with a series of discharge points Within the safeguarding material `to promote the discharge of high voltage current from said leads.

5. Means for safeguarding electric igniters of blasting detonators against static charges otherwise capable of firing the igniter, including a safeguarding material of a nature having a high resistance to normal firing voltages, and a low i resistance to higher voltages of a static charge, independent shells arranged Wholly free of and beyond said igniters, a pair of electric leads for said igniters, said leads being separately directed `to and within the material in said shells respectively,the lead within the material of keach Aof said shells being bared and provided on theY bared area with electric discharge points, and means for grounding said shells.

6. A construction as defined in claim 5, vwherein the discharge points in each shell are in electrical continuity with the 4lead therein but free of .contact with the shell.

'7. Means for safeguarding a group of seriesconnected detonators having electrically-conf trolled firing means, including blasting leads common toall detonators, a grounded shell inde-` pendent Wholly free of and beyond said detonators, a safeguarding material in the shell and of a nature to-present a high resistance to voltages for intentionally ring the igniter and a low resistance to higher voltages of a static charge, electrical conductors leading from the blasting lead to and embedded as bared parts in said material, and connections from said respective shells to the leading and nal detonator of the series, the bared parts ofthe conductors are each provided With a series of discharge points free of Contact With the respective shells.

8. Means for safeguarding -a group of seriesconnectedl detonators having electrically-controlled firing means, including blasting leads common to all detonators, a grounded shell for each lead, eachshell being located Wholly free of and beyond .any detonator, a safeguarding material in each shell, said material being. of a nature to present a high resistance to detonator ring voltage and a low resistance to higher voltages of static charges, a conductor from each lead embedded as a bared -part in the material of the shell peculiar to that lead, anda conductor from each respective shell to the leading and nal detonator of the series, the bared parts of the conductors, in said shells being provided Wth'discharge points.

9. Means for safeguarding electric igniters of blasting detonators against accidental ringby electric currents or spark discharges Aproduced respectively in, or in the vicinity of, the firing means of the igniter by atmospheric electricity, comprising in combination a shell enclosing the igniter, a pair of electric leads for the igniter which are bared at parts, and a plugwhich surrounds said baredrparts, said plug consisting `of a coherer material of a character to present a high resistance to voltages of an intentional ring current for the igniter and -presenting under coherer action a low resistance to voltages of a current to beshunted, the bared parts being each formed to present a plurality of discharge points embedded in said plug.

10. Means for safeguarding electric igniters of blasting detonators against accidental firing by electric currents or spark discharges-produced respectively in, `or inthe vicinity of, the firing means of the igniter by atmospheric electricity, comprising in combination a shell enclosing the 4igniter, a pair of electric leads for the igniter which are bared at parts, and a Aplug which surrounds said bared parts, said plug consisting of a coherer material of a character to present a high resistance to voltages of an intentional ring current for the igniter and presenting under coherer action a -loW resistance to voltages of a current to be shunted, the bared parts being each formed to present a plurality of discharge points embedded in said plug, said discharge points` extending toward but terminating short of the shell.

11. Means for safeguarding electric igniters of blasting detonators vagainst accidental ring by electric currents or spark discharges produced respectively in, or in the vicinity of, the ring means of the igniter by atmospheric electricity, comprising in combination a shell enclosing the igniter, a pair of electric leads for the igniter which are bared at parts, and a plug which surrounds said bared parts, said plug consisting of a coherer material of a character to present a high resistance to voltages of an intentional ring current for the igniter and presenting under coherer action a low resistance to voltages of a current to be shunted, the bared parts being each formed to present a plurality of discharge points embedded in said plug, the bared parts of the leads being spaced apart within the plug a distance materially greater than the distance of either bared part and the adjacent shell.

12. Means for safeguarding electric igniters of blasting detonators of a type including a ring means, an igniter therefor, spaced electric leads for the igniter, each having a definite non-insulated length thereof spaced from the firing means, and an electrically-conductive shell surrounding the parts, said safeguarding means including a coherer mass of aluminum flakes completely filling a definite area in the length of the shell spaced from the ring means and in contact envelopment of non-insulated parts of the electric leads, said aluminum flake mass being normally nonconductive to a predetermined firing voltage and becoming conductive through coherer action to electrical charges of relative higher voltage passing through the leads.

13. Means for safeguarding electric igniters of blasting detonators of a type including a firing means, an igniter therefor, spaced electric leads for the igniter, each having a denite non-insulated length thereof spaced from the nring means, and an electrically-conductive shell surrounding the parts, said safeguarding means including a coherer mass of aluminum flakes completely lling a definite area in the length of the shell spaced from the firing means and in contact envelopment of non-insulated parts ofthe electric leads, said aluminum flake mass being normally nonconductive to a predetermined firing voltage and becoming conductive through coherer action to electrical charges of relative higher voltage passing through the leads, the space between the noninsulated portions of the leads within the safeguarding mass being materially greater than the distance between any one lead and the adjacent shell.

14. Means for safeguarding electric igniters of blasting detonators of a type including a ring means, an igniter therefor, spaced electric leads for the igniter, each having a definite non-insulated length thereof spaced from the firing means, and an electrically-conductive shell surrounding the parts, said safeguarding means including a coherer mass of aluminum flakes completely filling a definite area in the length of the shell spaced from the ring means and in contact envelopment of non-insulated parts of the electric leads, said aluminum flake mass being normally nonconductive to a predetermined firing voltage and becoming conductive through coherer action to electrical charges of relative higher voltage passing through the leads, each non-insulated portion of a lead within the safeguarding mass being of increased electrical conductive transverse area, within the safeguarding mass to thereby reduce the conductive distance between each lead and the adjacent shell over the conductive distance between the leads.

15. A construction as defined in claim 14, wherein the increased electrical conductive transverse area of each lead is in the form of integral discharge points.

HANS JAY ROLFES. 

